The present invention relates to micro electro-mechanical (MEM) tunneling/capacitive sensors and in particularly to three axis sensors using multiple wafers which are bonded together eutectically.
The present invention provides a new process of fabricating multiple-axes rotation rate sensors on a single substrate using high performance single crystal silicon tunneling and capacitive devices. The prior art has demonstrated the ability to integrate multi-axes capacitive sensors on a single silicon (Si) substrate for 3-axes rotation measurements. See xe2x80x9cMicromachined Dual Input Axis Angular Rate Sensor,xe2x80x9d Thor Juneau, A. P. Pisano Solid-State Sensors and Actuator Workshop, Hilton Head, S.C., June 2-6, 1996, and xe2x80x9cMicrostructure Design of Angle Measuring MEMS Gyroscopes,xe2x80x9d Andrei M. Shkel, Ph. D. Thesis, Berkeley Sensor and Activator Center, 1999.) However, none of this prior art has addressed the combination of tunneling and capacitive sensors for a single-chip 3-axes sensor. The use of bulk-micromachining techniques and the techniques described in the above referenced patent applications allows for the combination of 2-axis tunneling rate gyros (for X and Y detection) and various types of 2-axis capacitive rate gyros on a single substrate.
One of the problems with prior art designs is that if three sensors are used, they need to be mechanically aligned. There is a need for a three axis sensor design in which the sensors are automatically aligned relative to each other as a result of the manufacturing process employed. This invention addresses this need.
Generally speaking, the present invention provides a method of making a micro electro-mechanical three-axis sensor wherein two orthogonally positioned cantilevered beam structures and a mating structure are defined on a first substrate or wafer and at least one contact structure and a mating structure are defined on a second substrate or wafer. The mating structure on the second substrate or wafer is of a complementary shape to the mating structure on the first substrate or wafer. A bonding or eutectic layer is provided on at least one of the mating structures and the mating structure are moved into a confronting relationship with each other. Pressure is then applied between the two substrates and heat may also be applied so as to cause a bond to occur between the two mating structures at the bonding or eutectic layer. Then the first substrate or wafer is removed to free the cantilevered beam structures for movement relative to the second substrate or wafer. The bonding or eutectic layer also provides a convenient electrical path to the cantilevered beam for making a circuit with the contact formed on the cantilevered beam.
In another aspect the present invention provides an assembly or assemblies for making a single crystal silicon three axis MEM sensor therefrom. A first substrate or wafer is provided upon which is defined at least two cantilevered beam structures and a mating structure. A second substrate or wafer is provided upon which is defined at least two contact structures and a mating structure, the mating structure on the second substrate or wafer being of a complementary shape to the mating structure on the first substrate or wafer. The two cantilevered beams are orthogonally to each other. Another sensor which is sensitive in a third orthogonal direction is also provided. A pressure sensitive bonding layer is disposed on at least one of the mating structures for bonding the mating structure defined on the first substrate or wafer with the mating structure on the second substrate in response to the application of pressure and heat therebetween.
The three axis sensor of the present invention provides for automatic self-alignment of the three sensors relative to each order in that semiconductor manufacturing type processes are used to manufacture the three sensors and thus the three sensors are lithographically aligned due to the use of masks to create most of the structures of the three sensors.